Olefinic Carbon Research Articles

Variations of soil organic matters and plant cuticular waxes along an altitude gradient in Qinghai-Tibet Plateau

This study aims to evaluate the variations of soil organic matter and plant leaf cuticular waxes along an altitude gradient at two mountains in the east side of the Qinghai-Tibet Plateau. Surface soils were sampled along an altitude gradient (2600, 3000, 3400, 3800 and 4200 m). We analyzed the soil total organic carbon (TOC), dissolved organic carbon (DOC), soil lipids and leaf cuticular waxes in Kobresia humilis which distributed at all tested altitudes. A sharp concentration increase of TOC was observed when altitudes increased, whereas the proportions of DOC in TOC at low altitudes (3000 m and 2600 m) were significantly higher than those at higher altitudes. Altitudes also influenced the molecular weight, humification degree, aromaticity, and hydrophobicity of DOC molecular. Though soils at higher altitudes relatively had higher abundance of odd carbon alkanes and even carbon alcohols, soil lipid concentrations showed no significant difference between altitudes. Relatively higher total wax coverage at high and low altitude was observed on leaves of K. humilis. The changes of altitudes at alpine ecosystem were associated with alterations of both quantity and quality of soil organic matter as well as leaf cuticular wax coverage, which contributed to their environmental adaptations.

The mechanisms of gallium-catalysed skeletal rearrangement of 1,6-enynes – Insights from quantum mechanical computations

The transition metal-catalysed skeletal reorganization of 1,6-enynes can lead to three types of products – a type I product occurring via the cleavage of the alkene C–C bonds and the migration of the terminal alkene carbon to the terminus of the alkyne; a type II product arising from cleavage of both the double and the triple bonds followed by insertion of the terminal alkene carbon into the alkyne C–C triple bond; and a type III product which is obtained when there is a cleavage of the olefinic bond followed by formation of two new bonds from each carbon to each of the acetylenic carbons. The course of these reactions is highly dependent on the metal catalyst used and type of substitution at the alkene and alkyne moieties of the enyne. In this mechanistic study of the re-organization of 1,6-enynes catalysed by GaCl3, performed at the DFT M06/6-311G(d,p) level of theory, the parent reaction selectively leads to the formation of the type I product through the formation of the open cyclopropane ring. The presence of substituents at the acetylenic moiety governs the preferred position of the metal along the alkyne bond within the pi-complex: with electron-withdrawing groups (EWGs), the metal prefers the terminal carbon while electron-donating groups (EDGs) lead to the metal preferring the internal carbon. EWGs at the alkyne moiety efficiently favour the formation of the type I product. Substituents at the olefin moiety alter the mechanism of the reaction which may favour the selective formation of the type I or III product depending on the type of substituent. EWGs at the olefinic moiety favour formation of the type III product when the alkyne moiety is unsubstituted whiles EDGs forms the type I product selectively. Solvent and temperature have no substantial effects on the energetic trends and product distribution. Hence, gas-phase calculations are deemed adequate for the problem at hand.

A molybdenum tris-(di-thiol-ene) complex coordinates to three bound cobalt centers in three different ways.

The synthesis and structural characterization of the mol-ecular compound (μ3-benzene-1,2-di-thiol-ato)hexa-carbonyl-bis-(μ3-1,1,1,4,4,4-hexafluorobut-2-ene-2,3-dithiolato)tricobaltmolybdenum, [Co3Mo(C4F6S2)2(C6H4S2)(CO)6] or Mo(tfd)2(bdt)(Co(CO)2)3 (tfd is 1,1,1,4,4,4-hexafluorobut-2-ene-2,3-dithiolate and bdt is benzene-1,2-di-thiol-ate), are reported. The structure of the mol-ecule contains the molybdenum tris-(di-thiol-ene) complex Mo(tfd)2(bdt) coordinated as a multidentate ligand to three cobalt dicarbonyl units. Each of the three cobalt centers is relatively close to molybdenum, with Co⋯Mo distances of 2.7224 (7), 2.8058 (7), and 2.6320 (6) Å. Additionally, each of the cobalt centers is bound via main-group donor atoms, but each one in a different way: the first cobalt atom is coordinated by two sulfur atoms from different di-thiol-enes (bdt and tfd). The second cobalt atom is coordinated by one sulfur from one tfd and two olefinic carbons from another tfd. The third cobalt is coordinated by one sulfur from bdt and two sulfurs from tfd. This is, to the best of our knowledge, the first structurally characterized example of a molybdenum (tris-)di-thiol-ene complex that coordinates to cobalt. The F atoms of two of the -CF3 groups were refined as disordered over two sets of sites with ratios of refined occupancies of 0.703 (7):0.297 (7) and 0.72 (2):0.28 (2).

Quantum Reality in the Selective Reduction of a Benzofuran System.

Two 2,3-disubstituted benzofurans (1 and 2), analogs of gamma-aminobutyric acid (GABA), were synthesized to obtain their 2,3-dihydro derivatives from the Pd/C-driven catalytic reduction of the double bond in the furanoid ring. The synthesis produced surprising by-products. Therefore, theoretical calculations of global and local reactivity were performed based on Pearson’s hard and soft acids and bases (HSAB) principle to understand the regioselectivity that occurred in the reduction of the olefinic carbons of the compounds. Local electrophilicity (ωk) was the most useful parameter for explaining the selectivity of the polar reactions. This local parameter was defined with the condensed Fukui function and redefined with the electrophilic (Pk+) Parr function. The similar patterns of both resulting sets of values helped to demonstrate the electrophilic behavior (soft acid) of the olefinic carbons in these compounds. The theoretical calculations, nuclear magnetic resonance, and resonance hybrids showed the moieties in each compound that are most susceptible to reduction.

Synthesis of Cyclic Carbonates from Olefin Oxides and Carbon Dioxide. Communication 2. Catalysis by Metal Porphyrin Complexes

The catalytic systems based on metal porphyrin complexes used for promoting the reactions of olefin oxides with carbon dioxide were reviewed. The metal porphyrin complexes were shown to be effective catalysts for carboxylation of epoxides. The catalyzed reactions of oxiranes with carbon dioxide in the presence of homogeneous and heterogeneous metal porphyrin complexes, including the reactions with the use of various promoting additives, were considered.

Temperature and Pressure Dependent Rate Coefficients for the Reaction of Ketene with Hydroxyl Radical.

The reaction of ketene with hydroxyl radical is drawing growing attention, for it is found to constitute an important step during the combustion of hydrocarbon and oxygenated hydrocarbon fuels, e.g., acetylene, propyne, allene, acetone, gasoline, diesel, jet fuels, and biofuels. We studied the potential energy surface (PES) of this reaction using B2PLYP-D3/cc-PVTZ for geometry optimization and composite methods based on CCSD(T)-F12/cc-PVTZ-F12 for energy calculations. From this PES, temperature- and pressure-dependent rate coefficients and branching ratios at 200-3000 K and 0.01-100 atm were derived using the RRKM/ME approach. The reaction is dominated by four product channels: (i) OH addition on the olefinic carbon of ketene to form CH2OH + CO, which is the most dominant under all conditions; (ii) H abstraction producing HCCO + H2O, which is favored at high temperatures; (iii) OH addition on the carbonyl carbon to form CH3 + CO2, which is favored at low pressures and high temperatures; and (iv) collisional stabilization of CH2COOH, which is favored at high pressures and low temperatures. With increasing temperatures, the overall rate constant koverall exhibit first negative but then positive temperature dependency, with its switching point (also the minimum point) at ∼400 K. Both product channel CH2OH + CO and HCCO + H2O are independent of pressure, whereas formation of CH3 + CO2 and collisional stabilization of CH2COOH are highly pressure dependent. Fitted modified Arrhenius expressions of the calculated rate constants are provided for the purpose of combustion modeling.

Genetic regulation of scytonemin and mycosporine-like amino acids (MAAs) biosynthesis in cyanobacteria

Scytonemin and mycosporine-like amino acids (MAAs) are important novel secondary metabolites synthesized by cyanobacteria to protect themselves from lethal ultraviolet (UV) radiation. Scytonemin, the extracellular polysaccharide sheath pigment is found in several cyanobacterial species and is a lipid-soluble dimeric pigment consisting of phenolic and indolic subunits linked through an olefinic carbon atom. Structure of MAAs consists of aminocyclohexenone or an aminocyclohexinimine chrompohore conjugated with the nitrogen substituent of an amino acid or its amino alcohol. MAAs are small, colorless water soluble compounds. These UV screening compounds are highly photostable photoprotectant and also serve as potent antioxidants. Multiple environmental signals influence scytonemin and MAAs synthesis and regulation of induction of these UV screening compounds is a part of complex stress response pathway. Hence, proper understanding of genetic regulation and biosynthesis of these microbial sunscreens would not only provide scientific insight in a major class of secondary metabolites but will also help in commercial production of these new age ecofriendly sunscreens.

Synthesis of Cyclic Carbonates from Olefin Oxides and Carbon Dioxide. Part 2. Catalysis by Porphyrin Complexes of Metals

The review paper deals with catalytic systems based on porphyrin complexes of metals used for stimulation of reactions of olefins and carbon dioxide. It is shown that these porlhyrin complexes may behave as effective catalysts for carboxylation of epoxides. Specific features of catalysis of the interaction between oxiranes and carbon dioxide in the presence of homogeneous and heterogenized porphyrin complexes of metals, including those comprising various promoters, are considered.

Spectroscopic and DFT assessment of bridging ligand effect on the structural and electronic properties of dinuclear iridium- and rhodium-based complexes

A series of chloro-, amido-, and methoxo-bridged dinuclear complexes of iridium(I) and rhodium(I) was synthesized, and their coordination properties were assessed. Density functional theory (DFT) calculations, and infrared and Raman spectroscopies were employed to examine the metal-olefin and metal-bridging group interactions. The outcome of these studies revealed that the nature of bridging ligands does influence the electronic properties of these metal complexes. They also revealed that the amido-bridged complexes exercised the least metal-olefin interaction, while the methoxo-bridged complexes exhibited the most. The p-character in the hybrid orbitals of olefinic carbons was calculated to increase upon coordination, and the extent of increase can be linked to the group electronegativity of bridging ligands. Vibrational spectroscopy, supported with theoretical DFT approach, was useful and found consistent in assessing the pi and combined (π + σ) metal-olefin interactions in these dinuclear complexes.

Insights into the N-Heterocyclic Carbene (NHC)-Catalyzed Intramolecular Cyclization of Aldimines: General Mechanism and Role of Catalyst.

One of the most challenging questions in the Lewis base organocatalyst field is how to predict the most electrophilic carbon for the complexation of N-heterocyclic carbene (NHC) and reactant. This study provides a valuable case for this issue. Multiple mechanisms (A, B, C, D, and E) for the intramolecular cyclization of aldimine catalyzed by NHC were investigated by using density functional theory (DFT). The computed results reveal that the NHC energetically prefers attacking the iminyl carbon (AIC mode, which is associated with mechanisms A and C) rather than attacking the olefin carbon (AOC mode, which is associated with mechanisms B and D) or attacking the carbonyl carbon (ACC mode, which is associated with mechanism E) of aldimine. The calculated results based on the different reaction models indicate that mechanism A (AIC mode), which is associated with the formation of the aza-Breslow intermediate, is the most favorable pathway. For mechanism A, there are five steps: (1) nucleophilic addition of NHC to the iminyl carbon of aldimine; (2) [1,2]-proton transfer to form an aza-Breslow intermediate; (3) intramolecular cyclization; (4) the other [1,2]-proton transfer; and (5) regeneration of NHC. The analyses of reactivity indexes have been applied to explain the chemoselectivity, and the general principles regarding the possible mechanisms would be useful for the rational design of NHC-catalyzed chemoselective reactions.

Atmospheric degradation of HCFO-1233zd(E) initiated by OH radical, Cl atom and O3 molecule: Kinetics, reaction mechanisms and implications

A degradation of trans-CF3CH=CHCl (HCFO-1233zd(E)) by reaction with OH radical, Cl atom and O3 molecule over the temperature range 200–1000 K has been studied employing the density functional theory. The potential energy surfaces accompnying the degradation have further been characterized in terms of single point energies derived from the coupled cluster CCSD(T) theory. Different possible pathways including H-abstraction, addition, isomerisation, dissociation and secondary reactions in absence and presence of O2/NOx are considered to elucidate the underlying mechanisms of the titled reactions. It has been shown that the initiation of degradation proceeds predominantly via addition to olefinic carbon with contributions from the direct H-abstraction channels being negligible as a result of the higher energy barrier. Calculated rate coefficients for the reaction of HCFO-1233zd(E) with OH was estimated to be 3.2 × 10−13 cm3 molecule‒1 sec‒1 whereas those for the reactions with Cl and O3 are predicted to be 3.7 × 10‒11 cm3 molecule‒1 sec‒1 and 50.0 × 10‒21 cm3 molecule‒1 sec‒1, respectively, which compare well with those from the earlier experiments. The present endeavor describes the atmospheric fate and oxidation processes of titled molecule and provides comprehensive data on the product branching ratios, atmospheric lifetimes and global warming potentials.

Comparison of preparation methods of iron-based catalysts for enhancing Fischer-Tropsch synthesis performance

Carbon supported iron catalysts for Fischer-Tropsch synthesis, with the same iron loading of ca. 35 wt.%, were prepared by pyrolysis process and incipient wetness impregnation methods. The effect of the preparation methods on the catalyst structure, catalytic properties, and the direct conversion of syngas via Fischer-Tropsch synthesis was investigated. The iron species, iron particle size and iron reducibility depended on the preparation method. The pyrolysis of homogeneous fusion yielded a unique core-shell structure with dispersed iron species embedded in a matrix of porous carbon. The FeOx/AC catalyst obtained by incipient wetness impregnation contained Fe2O3 species after calcination, while the core-shell structured catalyst obtained by pyrolysis process contained Fe3C species after calcination. The results show that the core-shell structure iron-based catalyst had higher extent of carburization and dispersion, which led to higher activity for Fischer-Tropsch reaction than that of other two catalysts obtained by different synthesis methods. Furthermore, the Fe3C@C catalyst promoted by alkali metals (Na, Mg, K, Ca) resulted in the increase of O/P ratio and low carbon olefin selectivity, and the decrease of methane selectivity.

The Lewis Pair Polymerization of Lactones Using Metal Halides and N-Heterocyclic Olefins: Theoretical Insights.

Lewis pair polymerization employing N-Heterocyclic olefins (NHOs) and simple metal halides as co-catalysts has emerged as a useful tool to polymerize diverse lactones. To elucidate some of the mechanistic aspects that remain unclear to date and to better understand the impact of the metal species, computational methods have been applied. Several key aspects have been considered: (1) the formation of NHO-metal halide adducts has been evaluated for eight different NHOs and three different Lewis acids, (2) the coordination of four lactones to MgCl2 was studied and (3) the deprotonation of an initiator (butanol) was investigated in the presence and absence of metal halide for one specific Lewis pair. It was found that the propensity for adduct formation can be influenced, perhaps even designed, by varying both organic and metallic components. Apart from the NHO backbone, the substituents on the exocyclic, olefinic carbon have emerged as interesting tuning site. The tendency to form adducts is ZnCl2 > MgCl2 > LiCl. If lactones coordinate to MgCl2, the most likely binding mode is via the carbonyl oxygen. A chelating coordination cannot be ruled out and seems to gain importance upon increasing ring-size of the lactone. For a representative NHO, it is demonstrated that in a metal-free setting an initiating alcohol cannot be deprotonated, while in the presence of MgCl2 the same process is exothermic with a low barrier.

Further spectral and chromatographic studies of ambergris

Jetsam ambergris, found washed ashore on beaches, is an environmentally modified form of a natural product of Sperm whales which sometimes develops a pleasant odour. Odorous samples have proved valuable in perfumery. Identification of jetsam ambergris by analysis of organic-soluble extracts by Fourier transform infra-red spectroscopy (FTIR) and of derivatised samples by gas chromatography-mass spectrometry (GC-MS) has already been shown. Here, we describe a different method, in which characteristic alkenic protons and carbon atoms of the major constituent ambrein, were identified in whole extracts using nuclear magnetic resonance spectroscopy (NMR). The advantages of employing NMR spectroscopy included rapidity, reduced losses of volatiles compared to GC-MS and detection of non-GC amenable constituents. However, the identities and quantities of co-occurring individual components (e.g. steroids) could not easily be assigned in the unfractionated extracts by NMR spectroscopy, whereas they were by GC-MS, so an approach combining FTIR, GC-MS and NMR spectroscopic methods is advocated.

Tribology Characteristics of HFO and HC Refrigerants with Immiscible Oils

Hydro fluoro olefin (HFO) and hydro carbon (HC) refrigerants have been considered for use in air-conditioning systems and refrigerators as low global warming potential (GWP) refrigerants. These refrigerants are determined the lubrication performance of the sliding parts in compressor. To clarify lubrication performance of unsaturated and saturated refrigerants for these low GWP refrigerants, seizure and wear tests were done in the compound of liquid refrigerant and refrigeration oil. Immiscible oils to refrigerants were used for lubrication. We confirmed that antiwear and antiseizure characteristics of unsaturated refrigerants (HFO-1234yf and R1270) are better than those of saturated refrigerants HFC-134a and R290.

Organic petrology and micro-spectroscopy of Tasmanites microfossils: Applications to kerogen transformations in the early oil window

The transformation of kerogen to hydrocarbons in the early stages of oil generation is critical for understanding the resource potential of liquid-rich shale plays. Organic petrology commonly is used for visual evaluation of type, quality, and thermal maturity of organic matter, but the relationship of visual petrographic changes to chemical transformations is not well characterized. To improve understanding of these processes, organic-walled microfossils of the unicellular green alga Tasmanites (composed of algaenan) in Upper Devonian Ohio Shale (Huron Member, Appalachian Basin) were analyzed by micro-spectroscopy techniques including micro-Fourier transform infrared (micro-FTIR), X-ray photoelectron (XPS), electron probe microanalysis (EPMA), and fluorescence. Immature to mid-oil window maturation sequences of core and outcrop samples with solid bitumen reflectance (BR) and vitrinite reflectance (VR) values ranging from 0.45 to 0.80%Ro were used. Hydrous pyrolysis was applied to low-maturity (BR: 0.25–0.39%Ro) Huron and time-correlative New Albany shale samples to create similar artificial maturation sequences for comparison. Micro-FTIR spectroscopy revealed a decrease in the CH2/CH3 ratio with increasing maturity, indicating Tasmanites aliphatic chains become shorter and more branched. Oxygenated functional groups decreased relative to aliphatic stretching bands and increased aromaticity was noted at the highest maturities. In samples that were pyrolyzed for 72h at temperatures of 300–320°C (BR: 0.56–0.68%Ro), Tasmanites showed similar trends, whereas at pyrolysis temperatures of 340°C and higher (BR>1.0%Ro), Tasmanites was pseudomorphed by accumulations of solid bitumen, carbonate and sulfide. Replacement of Tasmanites by these phases in hydrous pyrolysis experiments ≥340°C and its absence at higher maturities (peak oil, VR and BR≥0.9%Ro) in naturally matured samples, as documented in a previous study, implies that a large fraction of the algaenan component of original organic carbon is converted to petroleum during thermal maturation. XPS analysis indicated the molar proportion of aliphatic carbon increases with increasing thermal maturity, accompanied by decreases in oxygenated functional groups and olefinic carbon. EPMA of Tasmanites showed highest concentrations of S, with concentrations of redox-sensitive trace elements U, Mo, Ni and V generally at or below detection limits. Decrease in organic S with increasing thermal maturity may be related to cleavage of Tasmanites at CS linkages; however, this relationship was inconsistent and presence of adjacent or entrained nanoscale silicate or sulfide phases may impact measured trace element concentrations. Fluorescence microscopy and spectroscopy showed a red shift in spectral maxima and decreased emission intensities with increasing maturity, interpreted as due to non-radiative energy loss possibly because of increased aromaticity. Collectively, these results provide new insights into the in situ chemical transformations that accompany petrographic changes as oil-prone kerogen converts to petroleum with thermal advance from immature conditions into the mid-oil window.

A DFT Study on Mechanisms and Origin of Selectivity of Phosphine-Catalyzed Vicinal Acylcyanation of Alkynoates

The mechanisms of phosphine-catalyzed vicinal acylcyanation of alkynoates have been firstly investigated by density functional theory. Both PPhMe2- and PBu3-catalyzed reactions were enumerated and studied in detail. For each reaction, three possible pathways, including the direct pathway that leads to syn-selective product and two phosphine-catalyzed reaction pathways that lead to anti- and syn-selective products respectively, were considered in this work. The calculated results indicate that the most energetically favorable pathway contains five reaction steps: the nucleophilic attack on alkynoate by phosphine, the acylation by acylcyanide, the dissociation of CN group from acylcyanide, the addition of CN group to olefin carbon of alkynoate part, and the dissociation of phosphine and product. The last two steps are the key for the anti/syn-selectivity of reactions, and our computational results can reasonably explain the experimental observations. In addition, non-covalent interaction analysis was performed for exploring the origin of the anti/syn-selectivity. Moreover, the natural bond orbital (NBO) population and global reactivity index (GRI) analyses were also carried out to disclose the role of the phosphine catalyst in this kind of reaction. This work should be helpful for chemists to understand the detailed mechanisms and predict anti/syn-selectivity of this kind of vicinal acylcyanation.

The microwave spectrum and molecular structure of Ar-2,3,3,3-tetrafluoropropene

The microwave spectra of four isotopologues of the complex formed between argon and 2,3,3,3-tetrafluoropropene are obtained in the 5.6–18.4GHz region using a combination of broadband chirped pulse and Balle-Flygare cavity Fourier transform microwave spectroscopy. The argon atom is determined to occupy a position out of the symmetry plane of the tetrafluoropropene where it can interact most strongly with one of the out-of-plane fluorine atoms of the methyl group, carbon atom C2, and the fluorine atom attached to that olefinic carbon. In contrast to previously studied argon-haloethylene complexes, the argon atom is located almost directly above this latter atom instead of being offset from the atoms in the binding partner. Comparisons with analogous species suggests that the π electrons of the CC double bond play an important, but still not completely understood, role in determining the location of the argon while steric effects lead to strongly conserved distances between argon and the atoms to which it binds.

Selective Ethylene Oligomerization with Chromium-Based Metal–Organic Framework MIL-100 Evacuated under Different Temperatures

MIL-100(Cr) was synthesized and evacuated under different temperatures to generate a series of heterogeneous catalysts for ethylene oligomerization. These catalysts showed moderate catalytic activities for ethylene oligomerization but high selectivities to low carbon olefins C6, C8, and C10. Moreover, the oligomer distribution was different depending on the evacuation temperature. The XPS results showed the reduction of some CrIII active sites in the MIL-100(Cr) structure to CrII active sites, which made the catalysts show polymerization activities. The MIL-100(Cr)-250 catalyst evacuated at 250 °C exhibited the highest oligomerization and polymerization activities up to 9.27 × 105 g/(molCr·h) and 0.99 × 105 g/(molCr·h) respectively. The oligomerization selectivity to low carbon olefins C6, C8, and C10 was about 99%. The byproduct polymer from MIL-100(Cr)-250 belonged to linear polyethylene with ultrahigh molecular weight and broad molecular weight distributions. This work demonstrated that MOFs containing...

Probing the Peroxycarbenium [3+2] Cycloaddition Reactions with 1,2-Disubstituted Ethylenes: Results and Insights.

The causes for the title reaction to be limited to only the alkenes with an unsubstituted terminal alkenic carbon were explored. In some "failed" cases the cycloaddition products actually formed but rearranged concurrently. An oxygen atom or a N-Boc (Boc=tert-butyloxycarbonyl) group at the double bond was proven essential for acquisition of intact [3+2] cycloaddition products from 1,2-disubstituted ethylenes.